It is universally admitted that the Tuatara (
) occupies a unique place among living Reptiles. By some authorities it is placed in the order Rhynchocephalia, of which it is the sole living representative; others, indeed, have suggested that it should be included in the order Lacertilia, but even in this case it is regarded as being one of the least specialised forms. It is, then, a primitive member of the class, and is now only to be found on certain islands off the coast of New Zealand, being so near to extinction that it has been placed under protection by the Government of that country. Any additions to our knowledge of the anatomy of this form therefore seem worthy of being placed on record, particularly when, as will be discussed later, they have some bearing upon its relationship with allied forms. The animal is one of considerable importance, from the comparative point of view, and yet strangely enough no account of its blood vascular system as a whole has ever been given, either in general or in detail, nor is there, so far as I am aware, a satisfactory description of the general anatomy of the heart. Certain points concerning the arterial system have been described, but others have been left untouched, and the same may be said of the venous system. Indeed, in the case of the latter, although much comparative work has been done along certain lines, there is no good general account of the veins in any member of the order Lacertilia. This being so, it is hoped that the following pages, which contain a fairly full account of the blood vascular system in Sphenodon, will help to fill a noticeable gap in our knowledge of the circulatory system in the Reptilia. In conjunction with Prof. Dendy’s account (22) of the intra-cranial vascular system in the same species, it furnishes a more complete account of the blood-vessels than is available even for any of the Lacertilia.